Driver circuits are generally known from the state of the art for operating lighting means, in particular LEDs. A known driver circuit is supplied from an electrical supply, e.g. from an alternating voltage and particularly a mains voltage, and comprises a resonant circuit that is part of an LLC circuit, for example. A transformer is provided for transforming electrical energy across a galvanic barrier, from a primary side of the transformer or the driver circuit to a secondary side of the transformer or the driver circuit. The galvanic barrier therefore essentially divides the driver circuit into a primary side supplied from the electrical supply and a secondary side supplied from the secondary side of the transformer. The goal of the energy transfer is typically to supply the lighting means on the secondary side, particularly with an operating current. The LLC circuit preferably has two windings/spools of which one functions as the primary winding of the transformer, hereinafter also referred to as LLC transformer.
With the known driver circuits, there is however a problem when switching on the driver circuit, that the LLC circuit and thus the LLC transformer as a whole is started with a high frequency of 200 kHz, for example. With this high frequency, it can happen that the output voltage of the LLC transformer is so high that the voltage resulting on the lighting means exceeds the maximum voltage permissible for the lighting means. It can thus result in such an undesired voltage on the output of the driver circuit directly after starting the driver circuit and thus during the startup of the transformer due to a power curve of the resonant transformer. With a lighting means that has a relatively low breakdown voltage, such as with an LED, such a noticeable flash of light can be generated when turning on the driver circuit or during the startup of the LLC transformer, which constitutes an undesirable behavior for the user. It is also possible that the lighting means is damaged or destroyed as correspondingly high current flows through the lighting means.